Packers are used in oil and gas wells primarily to isolate different production zones. The packer is run downhole and set in place either hydraulically or mechanically, depending on the particular packer and the particular application. When the packer is in place, the annulus is blocked, and the production fluids are directed up the production tubing. On the packer, a slip mechanism provides a frictional hold between the packer and casing that helps keep the packer in place when subjected to high pressure and high thermal and applied forces.
Packers can be permanent or retrievable. Compared to a retrievable packer, a permanent packer is usually less expensive to manufacture and can be more resilient when set to high pressure and thermal and/or applied forces. Unfortunately, removing a permanent packer typically requires the packer to be milled out.
By contrast, a retrievable packer can be unset using a hydraulic or mechanical means, and the packer can then be pulled uphole with the production tubing or work string. Because the retrievable packer is designed to be removed, the retrievable packer is typically more complex and more expensive than a permanent packer. With this added complexity, the retrievable packer generally has more mechanical parts compared to a permanent packer, and this makes the retrievable packer more susceptible to mechanical failure upon or during retrieval. As expected, such mechanical failures can cause jams during retrieval, which can increase job times and expense.
Current slip mechanisms used in the art include T-style, hydro-style, and arrow-style slip mechanisms. When used on retrievable packers, these slip mechanisms have issues with both maximum load ratings and with retrieval problems after loading. Under higher loads, for example, the slip mechanisms can suffer mechanical failures, which results in difficulty retrieving the packer. Drilling operators seek to use slip mechanism in higher load applications and with fewer retrieval problems, but current slip mechanisms cannot meet these increasing requirements. Therefore, operators are limited by the maximum load ratings for current slip mechanisms.
FIGS. 1A-1B show a T-style slip mechanism 10 according to the prior art. The mechanism 10 includes T-style slips 20, a cone 30, and a cage 40—each of which dispose on a mandrel 14 of a retrievable packer 12 or the like. The T-style slips 20 have wickered ends 24 and T-shaped ends 28 interconnected by necks 22. Slip slots 42 in the cage 40 hold the T-shaped ends 28, while slots 32 in the cone 30 hold the wickered ends 24. In particular, the wickered ends 24 have shoulders or ledges 25 (FIG. 1B) that ride in grooves 35 in the cage's slots 32.
The T-style slips 20 set into the casing wall when the cone 30 is mechanically or hydraulically moved closer to the slip cage 40. For this reason, the slips' wickered ends 24 have ramped edges 27 that are pushed by the cone 30. Under load or during retrieval, the T-style slips 20 can suffer tensile failures, for example, near the shoulders 29 of the T-portion end 28 of the slip 20. Another type of failure common to the T-style slip mechanism 10 occurs when the forces at loading or retrieval (or a combination of the two) cause edges of the slip cage 40 and cage slot 42 to flair out.
Due to the failures that can occur, the T-style slip 20 can only have a certain width and amount of surface area that can set into the casing wall. For this reason, only the wickered end 24 of the slip 22 has wickers 26 to set into the case wall, while the T-shaped ends 28 have smooth surfaces. To increase their radial gripping area, the wickered end 24 could presumably be widened. Yet, any widening of the wickered end 24 would require the cone slip slots 32 to increase in size, and the neck 22 would be subjected to greater forces and have a higher likelihood of tensile failure.
To prevent flaring, wide portions 44 of the cage 40 may need to be present between each T-style slip 20 to main structural integrity of the mechanism 10. In the end, this limits the number of slips 20, the width of the slips 20, and the amount of wicker area 26 that can contact with the casing wall. To maintain the slip 20 in the retracted position during run-in and retrieval, the cone 30 and cage 40 stay in the un-set position during run-in or retrieval and keep the slip 20 from setting into the casing wall. Thus, the cage 40 must retain the T-portion end 28 of the slip 20, and the cone 30 must retain the wickered end 24 both during run-in and retrieval. The retention of the slip 20 in this way prevents the cone 30 from being locked into place in its retracted position during retrieval and puts the slips 20 held by the cone 30 and cage 40 under load.
FIGS. 2A-2B show a hydro-style slip mechanism 110 according to the prior art. The mechanism 110 includes hydro-style slips 120, a cone 130, and a cage 140—each of which dispose on a mandrel 14 of a retrievable packer 12 or the like. The hydro-style slips 120 fit around the mandrel 14 and have wickered faces 124a-b that fit through slip slots 142 in the cage 140. A spring 160 disposes in a central passage 122 along the length of the slip 120 and sits beneath a central band 144 in the slip slots 142. This spring, which is usually a leaf style spring, biases the slip 120 to a retracted condition when the cone 130 has been pulled out of the set position. As shown in the set position, however, the hydro-style slip 120 has wickers 126 on its outer face that can set into the surrounding casing wall (not shown).
To set the hydro-style slip 120 into the casing wall, the cone 130 is moved (typically by hydraulic activation) further beneath the slip cage 140 and also beneath the hydro-style slips 120. A ramped edge 137 on the cone 130 pushes against the ramped end 127 of the slip 120. Therefore, the cone 130 must slide beneath the slip cage 140 to push the slips 120 through the slip slots 142. This requires the thicknesses of the cone 130 and cage 140 to be appropriately configured, and this ultimately results in both the cone 130 and cage 140 being thinner due to space limitations.
For example, the cone 130 must be thick enough so that it does not collapse on the mandrel 14 under load, but it must be thin enough to slide under the slip cage 140. Likewise, the slip cage 140 must be thick enough to pluck the slips 122 during retrieval, but it must be thin enough to allow the cone 130 to slide underneath it. The thicknesses of the slips 120 too must be balanced with how much thickness and radial area is available from the cone 130 and cage 140. Based on the limited amount of cross-section available downhole, the thicknesses of the slips 120, cage 140, and cone 130 can ultimately limit how much load the hydro-style slip mechanism 120 and, hence, the packer 110 can handle.
Although the slip slots 142 are spaced equally around the cage 140, the hydro-style slips 122 are separated by portions 143 of the cage 140 between the slip slots 142 to maintain structural integrity. This can limit the amount of wicker face 124 that can contact with the casing wall.
There are typically three modes of failure common with hydro-style slip mechanisms 110. Loading forces can cause the slip 120 to ride on top of the cone 130 during loading, or the cone 130, due to its reduced thickness, can collapse on the mandrel 14. Additionally, the slips 120 can rip through the slip cage 140 due to its reduced thickness. These failures can occur when the slip mechanism 110 is set in place or during retrieval and typically occur more frequently with increasing loads. As expected, such failures can result in greater retrieval times and greater job expense.
FIGS. 3A-3B show an arrow-style slip mechanism 210 according to the prior art. This mechanism 210 includes arrow-style slips 220, a cone 230, and a cage 240—each of which dispose on the mandrel 14 of a retrievable packer 12 or the like. The arrow-style slips 220 fit around the mandrel 14 and have wickered ends 224 and fitted ends 228 interconnected by necks 222. The fitted ends 228 fit in comparably shaped slots 242 in the cage 240, while the necks 222 fit under a shoulder area 244 on the edge of the cage 240.
The arrow-style slip 220 sets into the casing wall when the cone 230 is mechanically or hydraulically moved closer to the slip cage 240. In particular, the wickered end 224 of the slip 220 includes a ramped edge 227 on its inner side. When the cone 230 is moved toward the cage 240, the cones ramped edge 237 engages the slip's ramped ends 227, pushing the slip's wickered end 224 into the casing wall. When the slip 220 sets, the wickers 226 on the slip's wickered end 224 set into the surrounding casing wall (not shown). Whether the slips 220 are set or not, the cage 240 remains connected to the fitted ends 228 of the arrow-style slip 222 by virtue of these slip slots 242.
Two failure modes are typically observed for this type of slip mechanism 210. First, the slips 220 experience tensile failures or bending in the thinned neck 222. Second, the slip cage 240 can flair out or even rip near the slots 242 and the distal edge or shoulder area 244. These failures can result in greater retrieval times and greater job expenses.
To overcome issues with flaring of the cage 240 and the like, the cage 240 requires portions 243 to be present between the arrow-style slips 220. These portions 243 help give then cage 240 structural integrity around the slip slots 242. Although the slips 220 are spaced equally around the mechanism 210, the need for these portions limits the area of slip wickers 226 that contact with the casing wall.
Moreover, the slip 220 uses the thinned neck 222 that fits under the shoulder area 244 of the cage 240 where a conical spring 260 biases the slip 220 to a retracted position. When the slip 220 is set and under load, the neck 222 of the slip 220 bears load of the tool, as the load is transferred through the back face of the slip 220, through the slip neck 222, and finally through the teeth 226 and into the casing. This loading through the neck 222 can weaken the slip 220 for retrieval.
During retrieval, the shoulder 225 between the neck 222 and fitted end 228 engages against the shoulder area 244 on the cage 240. The thickness of the thinned neck 222 of the slip 220 must be balanced with the width of the slip's wickered end 224. This is because additional width of the wickered end 224 may increase the load on the neck 222. The thickness of the neck 222 must also be configured so that the slip 220 will not tend to bend at the neck 222.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.